Example 5: Control of concrete cracking: Estimation of the stress at reinforcement (Serviceability Limit State)

We will extend the
file created in Example 2 in order to calculate the stress at each rebar under
the loads defined below.

As many regulations
propose, the effect of cracking can be controlled by considering a reduced
reinforcement stress which is specified by other parameters, such as allowable
crack width, rebar diameters, rebar spacing etc.

The concrete
stress/strain curve is assumed to be linear.

Load cases

lc 1:

N = 0

My = -120 kNm

Mz = 0

lc 2:

N = 0

My = 37 kNm

Mz = 0

lc 3:

N = 20 kN

My = -54 kNm

Mz = 0

Solution with Cross Section Analysis & Design

Opening a file from disk

First of all we click
on the File menu and select Open in order to open the file we created in Example 2.

Unlock the model

Afterwards, if the
model is locked, we click on Edit -> Unlock model, in order to modify the
geometry of the cross section.

In the popup window,
we choose Yes to unlock the model.

Review of Analysis Parameters

We need to specify the
corresponding Analysis Parameters set by clicking Analysis -> Analysis Parameters.
We will use the default “SLS” set. The concrete stress block is linear and the
corresponding strain values are defined according to ACI 318. Strength
reduction factors φ do not need to be changed since we are performing an analysis in Serviceability Limit State
(stress calculation). The concrete tensile strength is ignored. You can
override these values by modifying any of the fields of the form.

Definition of load cases

We click on the
Analysis -> Deformed configuration -> Load cases menu item and next on
the button
in order to insert a new load case under the name “lc 1”. Afterwards we fill
the values for loads and make sure that the “SLS” Analysis Parameters set is
enabled. We can create the remaining load cases lc 2 and lc 3 likewise.

We click
OK to close the form.

Carry out the analysis

We just click Analysis
-> Deformed configuration -> Analyze, to perform the analysis.

Results

The results can be
obtained from the Analysis -> Deformed configuration -> Show results menu
item.

On this form, we
choose the “lc 1” load case at the top left corner, in order to view the
results related to the first defined load case.

The following data can
be found on this form.

Neutral axis location

Strain distribution

Equivalent force couple

Stress contour on the cross section area

Reinforcement forces/stresses

Stress information per material

As we
can see, the maximum stress values at reinfordcement are reported as expected
for rebars 1 to 4 (bottom layer reinforement) and have a value of 222.72 MPa.

By
the above mentioned way, we can obtain the results for the remaining load cases
“lc 2” and “lc 3” by changing the selected load case item at the top left
corner of the results form.

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ENGISSOL is an engineering software development and consulting company dedicated to provide robust and scientifically advanced software solutions in any field of civil and structural engineering across the globe. Software development and consulting services is what ENGISSOLdoes successfully for the last decade. Our team of experienced professionals is specialized in developing technical applications designed to meet your specific business needs and requirements and our many years of experience help us deliver you solutions that even exceed your initial expectations. The proof are the thousands of customers who trust us.